Do you know why the sea is salty?

Seas and oceans cover about 70% of the surface of our planet, and about 97% of the water on Earth is salty. If all the salt could be extracted from the ocean and evenly distributed over the land, a layer over 166 meters thick would form, which is approximately the height of a 40-story office building. Why so much salt?

Well, it enters the seas and oceans from land. When clouds form rain, it accumulates carbon dioxide from the atmosphere and becomes slightly acidic, that is, capable of oxidizing various substances upon contact with them.

Rainwater falls to the ground and flows over the surface. At the same time, it destroys rocks and stones and absorbs a small amount of salt and other dissolved minerals. Then the rains are collected in streams and rivers. At this stage, the water is still fresh. It contains very little salt, at least not enough to make it undrinkable.

However, water in streams and rivers continues its journey, picking up more salts and minerals along the way, a process called erosion. In the end, salts and minerals, along with the river, enter the ocean, where they accumulate.

But salts end up in seawater not only due to river flows, but also as a result of underwater hydrothermal and volcanic activity. When magma in deep volcanoes and fissures heats up water, it begins to dissolve salts and minerals from the surrounding rocks. Then sea water, saturated with dissolved elements, rises from the bottom and additionally saturates the oceans with various salts.

The main salt in sea water is sodium chloride, common table salt.

But salts of magnesium, calcium, potassium and many other chemicals are also present in the sea. A significant part of them is needed for ocean life. Certain elements such as iron, zinc and copper absorbed from the water by marine organisms. However, the main components of table salt - sodium and chloride - remain in the ocean, because they are not very in demand among underwater microorganisms, algae, shellfish and other living creatures.

You may ask: Why haven't the oceans become salty enough over billions of years to be uninhabitable? Just salt with time settles in the form of deposits at the bottom. This provides balance and prevents the water from being too salty.

The salinity of the seas and oceans is of great importance for life on Earth. Sea water, rich in minerals and salts, is a source of essential chemicals for many species of fish, algae and other marine organisms. It is algae, not trees, that take on the main burden of photosynthesis and development oxygen in our planet's atmosphere.

In addition, the salinity of ocean water is also affects on its thermodynamic properties. More saline water has a lower freezing point and a higher density, which allows efficient thermal circulation in the ocean and has a huge impact on climate conditions.